1. Field of the Invention
This invention relates to a novel ceramic composition having a ulterior strength at high temperatures, a process for producing the same and a molding auxiliary.
2. Description of the Related Art
Aluminous ceramics are high strength ceramics having currently most advanced use applications and also one kind of ceramics having superior mechanical strength, resistance to abrasion and chemically resistant stability and also are expected to have more extended use applications.
Aluminous ceramics are well known in that they are superior in heat resistance and mechanical strength to other materials, but have a drawback in the aspect of moldability. Aluminous ceramics, too, are not exceptional in the above fact. Thus, in order to impart moldability to ceramic power and cause the resulting molded body to have strength, molding auxiliaries have been needed.
According to the prior art, polyvinyl butyral, polyvinyl alcohol and the like have been used as a molding auxiliary for the ceramic powder, and a release agent, a deflocculant and the like have been added thereto. The quantity of these molding auxiliaries used varies depending upon the molding process or technique, but in general, there is a tendency that the more complicated the shape of the resulting molded product, the greater the quantity of the molding auxiliary used.
Further, it is necessary for the product molded when using the auxiliary, to remove the used molding auxiliary in advance of its sintering, and in general, removal by thermal decomposition, referred to as degreasing is applied. As to the degreasing step, the more the quantity of the binder used and the more complicated the shape of the resulting molded product, the longer is the step required. Further, faults such as bulges, cracks, etc. occur very often.
Further, aluminous ceramics have superior mechanical strength and have been expected to be useful as a structural material, as described above. However, in recent years, a material having high strengths at high temperatures has been required, and actually, more expensive silicon nitride, silicon carbide and further, composite materials have been sought as the material. Aluminous ceramics have a high strength at room temperature, but they exhibit notable reduction in the strength at 1,000.degree. C. or higher and the strength at 1,200.degree. C. is reduced about 1/3 to 1/4 the strength at room temperature.